Aging is characterized by peripheral (muscle) insulin resistance. However, the molecular mechanisms responsible for skeletal muscle insulin resistance in aging are not well understood. Elucidation of the signaling mechanism/s that mediate insulin resistance in aging will help design novel ways to prevent/reverse the defect in insulin action and this will result in a reduced risk of developing type 2 diabetes. Cell culture experiments and in vivo studies in rodents and humans strongly suggest that increased activity of the IKK/lkB/NFkB pathway plays a major role in the pathogenesis of muscle insulin resistance. Recently, we established that aging is associated with increased IKK/lkB/NFkB signaling. Taken together, these data suggest that increased activity of the IKK/lkB/NFkB pathway may be responsible for insulin resistance in older subjects. However, the mechanism responsible for increased activity of the IKK/lkB/NFkB pathway in muscle from older human subjects is not known, and it remains to be determined whether excessive IKK/lkB/NFkB stimulation in muscle is responsible for the impairment in insulin signaling/sensitivity in older subjects. Using the insulin clamp with muscle biopsies, DEXA, magnetic resonance spectroscopy/imaging, real-time PCR, and in vivo and in vitro evaluation of mitochondrial function, we plan to test the hypothesis that elevated intramyocellular lipid content and/or reactive oxygen species (ROS) levels in muscle, resulting from decreased mitochondrial function, are responsible for aging-related increases in IKK/lkB/NFkB signaling in muscle from older subjects. We also recently observed that physical training inhibits IKK/lkB/NFkB signaling in middle-aged subjects. We also hypothesize that training can reverse insulin resistance in aging muscle by inhibiting IKK/lkB/NFkB signaling. The following Aims are proposed: 1) Determine whether decreased mitochondrial function, elevated intramyocellular lipid content, and/or increased ROS levels, lead to increased activity of the IKK/lkB/NFkB pathway in muscle from older subjects;Aim 2) Determine whether elevated IKK/lkB/NFkB signaling in aging muscle leads to insulin resistance by inhibiting the insulin signaling pathway;Aim 3) Determine whether exercise training decreases elevated IKK/lkB/NFkB signaling and improves insulin sensitivity in aging muscle. These studies will yield new insights into the causes of insulin resistance that occur with aging and how training helps to prevent/reverse them.